1. Technical Field
This invention relates generally to hydrodynamic non-contacting seals and particularly to a hydrodynamic non-contacting face seal for use in rotating machinery such as gas turbine engines.
2. Background Information
Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air which is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture which is exhausted from the engine's combustor. The compressor and turbine employ rotors which typically comprise a multiplicity of airfoil blades mounted on or formed integrally into the rims of a plurality of disks mounted on a shaft. Typically, such shafts are rotatably supported on bearings lubricated with a lubricant such as oil, disposed within the interior of a bearing compartment which is pressurized with a mixture of air and lubricating oil. It is well known to provide bearing compartments with mechanical seals, such as non-contacting face seals, as a means to minimize the escape of the lubricating fluid from the compartments' forward and aft ends. The air outside of these ends is typically at a higher pressure than the pressure of the air-oil mixture inside the compartment. Such face seals typically employ a stationary sealing member which is mounted within the bearing compartment and a rotatable sealing member or seal ring mounted on the rotor shaft. The stationary sealing member is usually provided with a smooth, continuous (uninterrupted) sealing surface which is disposed in face-to-face opposed relationship to a sealing surface of the rotatable seal ring. The sealing surface of the rotatable seal ring is often equipped with hydrodynamic features such as with a pattern of spiral grooves. Fluid such as the above-noted air enters the grooves and the space between the seal members from outside the compartment. The sealing fluid is pumped within the spiral grooves, raising the pressure thereof such that the elevated pressure of the fluid within the grooves forms a fluid barrier between the two sealing members thereby restricting the leakage of the air-oil mixture from inside the compartment into the gap between the sealing members. It will be appreciated that the pumping characteristics of the grooves to provide the elevated pressure fluid seal between the two sealing members is a function of the characteristics of the fluid outside the compartment, the rotational speed of the rotatable sealing member and the geometry of the grooves themselves. Since rotating machinery such as gas turbine engines are required to operate at a wide range of rotational speeds, the ability of the grooves to pump adequately to provide the pressurization of sealing fluid between the sealing members over such a wide range of rotational shaft speeds is imperative. Prior art attempts to provide adequate sealing with the above-noted spiral groove face seals throughout a wide range of operating conditions of the rotating machinery have taken the form of multiple spiral groove patterns in the rotating seal member or a mixture of spiral seal patterns with other groove configurations such as circumferential grooves and radial grooves which have proven less than adequate to provide the necessary sealing over a wide range of operating speeds.
For these reasons, it is desired to provide an improved hydrodynamic non-contacting face seal suitable for use in the bearing compartments of gas turbine engines which will provide adequate sealing throughout the wide ranges of operating speeds required of such gas turbine engines.